To achieve a high system throughput in a communication system using an OFDM scheme, a method is under study whereby subcarriers are divided into a plurality of resource blocks (RB: which refers to a group composed of a plurality of subcarriers and serve as an allocation unit during scheduling) and users are allocated to the resource blocks according to a channel quality indicator (CQI) for each resource block using time-frequency scheduling.
In order to effectively obtain a multi-user diversity gain through time-frequency scheduling, one resource block is set smaller than a correlation bandwidth. On the other hand, when the bandwidth of a resource block becomes small, the number of resource blocks increases. Effective frequency scheduling requires a CQI to be reported on a per resource block basis, and therefore when the number of resource blocks increases, the amount of CQI report (amount of information) increases and the overhead in uplink also becomes large. Furthermore, when the number of communication terminals increases, the proportion of CQI's in an uplink signal also increases. Moreover, M-ary modulation further increases the number of selectable parameters, and therefore the amount of CQI report increases.
For example, Non-Patent Document 1 discloses a technique of reducing the amount of CQI information in uplink by limiting the number of resource blocks (number of RBs) to be reported.
One such method selects N resource blocks in descending order of received quality as resource blocks for which CQI's are to be reported and reports CQI values corresponding to resource block identifiers (RB-ID) which specify those resource blocks. Furthermore, another method puts together a plurality of resource blocks, sets an RB group for CQI report and reports from each communication terminal only CQI's of resource blocks included in the RB group. This limits the number of resource blocks targeted for CQI report, and can thereby reduce the amount of CQI report.
When a transmission rate is relatively low and the number of resource blocks to which data is allocated is small, this technique can effectively reduce the amount of CQI report in uplink for communication terminals to which resource blocks are allocated preferentially without substantially losing a multi-user diversity gain.    Non-Patent Document 1: “Physical Channels and Multiplexing in Evolved UTRA Downlink” (R1-050590), 3 GPP TSG-RAN WG1 contributory document, NTT DoCoMo, June 2005